46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015;
Columbus, Ohio
Session H4: Invited Session: Nonlinear X-ray Science
10:30 AM–12:30 PM,
Wednesday, June 10, 2015
Room: Union DE
Chair: James Cryan, SLAC National Accelerator Laboratory
Abstract ID: BAPS.2015.DAMOP.H4.1
Abstract: H4.00001 : Multi-photon ionization of atoms in intense short-wavelength radiation fields
10:30 AM–11:00 AM
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Abstract
Author:
Michael Meyer
(European XFEL GmbH)
The unprecedented characteristics of XUV and X-ray Free Electron Lasers
(FELs) have stimulated numerous investigations focusing on the detailed
understanding of fundamental photon-matter interactions in atoms and
molecules. In particular, the high intensities (up to
10$^{\mathrm{16\thinspace }}$W/cm$^{\mathrm{2}})$ giving rise to non-linear
phenomena in the short wavelength regime. The basic phenomenology involves
the production of highly charged ions via electron emission to which both
sequential and direct multi-photon absorption processes contribute. The
detailed investigation of the role and relative weight of these processes
under different conditions (wavelength, pulse duration, intensity) is the
key element for a comprehensive understanding of the ionization dynamics.
Here the results of recent investigations are presented, performed at the
FELs in Hamburg (FLASH) and Trieste (FERMI) on atomic systems with
electronic structures of increasing complexity (Ar, Ne and Xe). Mainly,
electron spectroscopy is used to obtain quantitative information about the
relevance of various multi-photon ionization processes. For the case of Ar,
a variety of processes including above threshold ionization (ATI) from 3p
and 3s valence shells, direct 2p two-photon ionization and resonant 2p-4p
two-photon excitations were observed and their role was quantitatively
determined comparing the experimental ionization yields to ab-initio
calculations of the cross sections for the multi-photon processes. Using Ar
as a benchmark to prove the reliability of the combined experimental and
theoretical approach, the more complex and intriguing case of Xe was
studied. Especially, the analysis of the two-photon ATI from the Xe 4d shell
reveals new insight into the character of the 4d giant resonance, which was
unresolved in the linear one-photon regime. Finally, the influence of
intense XUV radiation to the relaxation dynamics of the Ne 2s-3p resonance
was investigated by angle-resolved electron spectroscopy, especially be
observing the intensity dependent variation of the angular distribution
patterns for the sequential ionization process.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2015.DAMOP.H4.1